I. Field of the Invention
The present invention relates generally to fuel pumps and, more particularly, to a fuel pump for a direct injection spark ignition engine.
II. Description of Related Art
Many modern automotive vehicles utilize a direct injection internal combustion engine in which the fuel is injected directly into the combustion chamber by a fuel injector rather than upstream from the intake valves to the combustion chamber. Since the fuel is injected directly into the combustion chamber, the direct injection engines enjoy a higher efficiency and better fuel economy than other types of internal combustion engines.
Since fuel is injected directly into the engine cylinders or combustion chambers, the fuel supply must necessarily be provided at a high pressure sufficient to overcome the pressures existing within the interior of the combustion chambers. Typically, a fuel pump supplies fuel from a source of fuel, such as a fuel tank, to a high pressure fuel injection rail. The fuel injection rail is then fluidly connected to the individual fuel injectors that are mounted on the engine block. The opening and closing timing for each of the fuel injectors for the engine is then controlled by an electronic control system for the vehicle.
The previously known fuel pumps for the spark ignition by direct injection (SIDI) engines typically included a housing having both a fluid inlet connected to the fuel tank and an outlet connected to the fuel injection rail. A plunger is then reciprocally driven by a cam in synchronism with the engine in a pump chamber within the interior of the housing between the inlet and the outlet.
In order to control the fuel flow from the pump inlet to the outlet, the fuel pump includes an inlet valve which is conventionally driven between an open and a closed position by a solenoid. A one way check valve is then positioned within the outlet to permit fuel flow from the pump chamber and through the outlet to the fuel rail.
In operation, the inlet valve is opened and closed by energization of the solenoid. When the plunger is retracted from the pump chamber, the inlet valve is opened by the solenoid thus allowing the plunger to induct fuel from the fuel tank into the pump chamber. Conversely, as the plunger is extended or driven into the pump chamber, the inlet valve is closed so that the fuel pressurized by the inward movement of the plunger opens the outlet valve and pumps the pressurized fuel through the one way outlet valve and into the pressure rail.
One disadvantage of these previously known SIDI fuel pumps, however, is that the overall fuel system is quite noisy in operation, especially at low engine speeds. The noise from the fuel system is undesirable for the comfort of the occupants of the vehicle.
Although there are many sources of noise in the fuel system for a SIDI engine, one major cause of engine noise results from the fuel pulsations caused by the reciprocating plunger in the overall fuel system. These fuel pump pulsations occur not only in the fuel pump, but also through the remainder of the fuel system including the fuel rails.
A second major source of noise for the SIDI engines is attributable to noise from the opening and closure of the inlet valve for the fuel pump. The opening and/or closure of the inlet valve causes an anchor in the solenoid valve to impact against a stationary core in the solenoid valve. This impact between the anchor and the core causes a clicking sound which is particularly audible at low engine speeds.